Atsushi Yamaoka

A Novel Error Separation Technique for Quadrature Modulators and Demodulators

In recent mobile communication systems, impairments in analog circuits cannot be disregarded due to achieving high performance. Errors in analog circuits consist of a distortion of a power amplifier(PA), gain and phase imbalance in a quadrature modulator (QMOD) and a quadrature demodulator (QDEMOD), dc offset, frequency offset, and so on. Because of high accuracy of compensation, many techniques of error compensation by using a digital signal processing have been studied recently. Digital predistorter (DPD), which can eliminate odd-order distortion caused by PA nonlinearity, is one of the compensation techniques, but in the case that direct conversion architecture is used in a loop-back path, errors in QMOD and QDEMOD affect the performance of DPD. In this paper, we propose a novel technique for error separation for QMOD and QDEMOD error estimation by adding a phase shifter to the conventional DPD architecture

Experimental performance evaluation of IQ imbalance and DC offset estimation and compensation technique for 3GPP LTE base station

In the case of recent wireless communication systems, the need to achieve high performance means that impairments in analog circuits cannot be disregarded. In view of the need for highly accurate compensation, many error compensation techniques using digital signal processing have been studied recently. Digital predistorter (DPD), which can eliminate odd-order distortion caused by PA nonlinearity, is one of the compensation techniques. However, in the case that direct conversion architecture is used in both a forward path and a loop-back path, errors in a quadrature modulator (QMOD) and a quadrature demodulator (QDEMOD) affect the performance of DPD. Previously, we proposed an error estimation technique for a QMOD and a QDEMOD that uses a variable phase shifter and evaluated its performance by an experiment using a narrow-band signal. In this paper, we evaluate the performance of the error estimation technique using the signal based on the 3GPP Long Term Evolution (LTE), whose bandwidth is wider than that in the previous experiment. The results show that image rejection ratio (IRR) after compensation is −59dBc and error vector magnitude (EVM) is −52dBc at the output of the QMOD.

Experimental performance evaluation of error estimation and compensation technique for quadrature modulators and demodulators

In recent mobile communication systems, impairments in analog circuits cannot be disregarded owing to the need to achieve high performance. Errors in analog circuits consist of a distortion of a power amplifier(PA), gain and phase imbalance in a quadrature modulator(QMOD) and a quadrature demodulator(QDEMOD), dc offset, frequency offset, and so on. Because of high accuracy of compensation, many techniques of error compensation by using digital signal processing have been studied recently. Digital predistorter(DPD), which can eliminate odd-order distortion caused by PA nonlinearity, is one of the compensation techniques. However, in the case that direct conversion architecture is used in a loop-back path, errors in a QMOD and a QDEMOD affect the performance of DPD. Previously, we proposed an error estimation technique for a QMOD and a QDEMDO by using a variable phase shifter and evaluated the performance through computer simulation. In this paper, we evaluate the performance through an experiment by image rejection ratio(IRR) and error vector magnitude(EVM) in the case that the output of a QMOD is directly connected to the input of a QDEMOD. The results show that IRR improvement after compensation is 10 dB at the output of the QMOD and EVM improvement after compensation is 10 dB at the output of the QMOD and 20 dB at the output of the QDEMOD.

Simplified Temperature Compensation Technique for Digital Predistorter Using Fixed Coefficients

An adaptive digital predistorter (ADPD) promises accurate nonlinear compensation and can automatically follow the change of output power of PA, a gain of transmitter consisting of DAC, mixer, PA, etc., and nonlinearity of PA by temperature fluctuation. However, an ADPD needs costly, large-power-consuming, and bulky equipment for calibration-loop. To overcome these drawbacks, we propose a simplified digital pre-distorter (DPD) using fixed coefficients with a variable gain amplifier (VGA), which requires no adaptive estimation block. The proposed DPD alleviates the performance degradation due to the change in temperature. The results show that error vector magnitude (EVM) of 2% and adjacent channel power ratio (ACPR) of -48dBc can be achieved from -20 to 70 degrees Celsius using single-carrier 64-QAM signal.